Ive been very busy with Uni work (stifles a semi yawn..theres no electronics this year. our hardware lecturer left and theres a cupboard full of Arduibos not being used )
Also been learning about FPGAs. I've got a Papilio one 500K and a Logicstart board. But about SN-Voice..
I tried everything to get the chip to stay in and couldn't get it to stay.
So I unsoldered the Sdip socket and replaced the chip with a 28 pin dip ( I got it chea from China.
Now I have everything working fine including PWM but now the LFO doesn't work :..(
I've looked around the circuit and can't see anything unconnected.
When I change the LFO Range it makes a small difference and the tone goes down maybe half a semitone but that is all.
Is it possible that DIP packages have a slightly different LFO configuration??
I wouldn't have thought so but... hmmm I am stumped on this one..._________________There's a crack in everything...Thats how glue manufacturers make a living.

Lets start by having you explain the patch first, then we can zero in on what we think is happening.

Aside from the LF444 buffered/amplified//offset LFOOUT, which buffers the LFORANGE capacitor, there is not much else involved. I know the LFORANGE is also sent to a modulation selector switch via a 4.7M resistor which end up using the LFO to "PWM" the output.

Hi Bill! Sorry I am a bit slow in my responses. Work stops me..
I see pins 20 & 21 of the 76477 connect to LFO. I have an oscilloscope. what should I be looking out for?_________________There's a crack in everything...Thats how glue manufacturers make a living.

Still no joy after coming back to the circuit, changing the 4.7Mohm resistor, checking all junctions connections etc etc. If it comes to it I will build a small LFO circuit to stick on the underside of the face (theres no room anywhere else.) I have another one of the 76477 chips from the same supplier and I have successfully breadboarded a simple VCO/LFO circuit which works fine. Its a mystery._________________There's a crack in everything...Thats how glue manufacturers make a living.

My SN voice has been sitting exposed for some time now. The LFO stopped working. I have tested as much as I can and have now completely disconnected the board from the module. I would like to know if it might be possible that in changing the 76477 chip, I could've damaged a via associated with the LFO?? Does the LFO have any vias that could be affected??

I'm going to take the chip off the board with a sucker and have a good examine again.....
If you read this Bill or anyone who knows the PCB
outside in, please let me know,
thanks again,
Steve._________________There's a crack in everything...Thats how glue manufacturers make a living.

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